Works only while debugger is attached

However, I'm facing a very strange behaviour : In my test project, but also in your "sample2 project" , "Acquire()" only works if application is launching from debugger. with CTRL+F5 or in release mode,
"Acquire()" returns : "TwainException: DG DAT MSG out of expected sequence. ConditionCode = SeqError; ReturnCode = Failure;"